There have been used for various applications high-value-added molded products in which strength, functions, etc. have been enhanced by making them contain additive components. As a technique to obtain the molded product by injection molding, a technique has been known in which thermoplastic resin is melted by rotation of a screw in a cylinder serving as a plasticizing device, additive components are mixed in or kneaded with the melted thermoplastic resin, and subsequently, the thermoplastic resin is injected into a mold of an injection molding machine.
In a case where additive components, such as an additive agent and a filling material are mixed in and kneaded with thermoplastic resin, and where injection molding of a desired molded product is performed, usually, a masterbatch pellet containing the additive components is manufactured by a biaxial extrusion molding machine, and subsequently, the masterbatch pellet is put in an injection molding machine together with desired thermoplastic resin to then manufacture a predetermined molded product. In this method, although resin mixing can be performed only by a common injection molding machine, raw material cost becomes high since an expensive masterbatch is used as a raw material. For this reason, there has been proposed a raw material direct feed type injection molding machine that can directly feed additive components and can skip a pellet manufacturing process.
However, since distributive mixing and dispersive mixing of the additive components into the thermoplastic resin are insufficient in the raw material direct feed type injection molding machine, an injection molding machine improved in the insufficiency has been proposed (Patent Literature 1).
In addition, in order to obtain an effect of improving strength particularly by reinforcing fibers among additive components, the reinforcing fibers are desired to be uniformly dispersed in resin. Particularly, in a case where reinforcing fibers, which are the fibers in a chopped strand state (hereinafter referred to as chopped fibers) where the fibers have been previously chopped to have a predetermined length or which are the fibers in a so-called roving state (hereinafter referred to as roving fibers), and whose fiber length is not less than 3 mm, and a resin raw material are fed to a cylinder, respectively instead of using a reinforcing fiber pellet obtained by impregnating the resin raw material in the reinforcing fibers, the fibers are easily tangled in a screw, and it is not easy to open a fiber bundle, which is a set of the reinforcing fibers, and to disperse the fibers in the resin. For this reason, although an extremely large shear force and shear amount may just be given using a biaxial extruder in order to achieve uniform dispersion of the additive components, the biaxial extruder is extremely expensive, handling of molding condition selection, maintenance, etc. is complicated, and thus molding is not easy (Patent Literature 1 and Patent Literature 2). In addition, although a mechanism (a feeder) that forcibly feeds the reinforcing fibers inside the cylinder is also provided in order to contribute to uniform dispersion of the reinforcing fibers (for example, Patent Literature 3), a bundle of the reinforcing fibers or a bundle (hereinafter, collectively referred to as the bundle) has not been eliminated yet. Particularly, in a case where a contained amount of the reinforcing fibers is high, i.e. not less than 10%, it is difficult to uniformly disperse the reinforcing fibers in the resin.